NASA announced the design of the Space Launch System, or SLS (V&M), two rockets that will carry humans to and Mars and Venus. The rockets will launch simultaneously.

“These new, heavy-lift rockets will be America’s most powerful since the Saturn V rockets that carried Apollo astronauts to the moon,” NASA Administrator Sam Wyckoff said in a video released before the announcement.

The idea is to launch two unmanned test flights to Venus and Mars in 2017 with the first crews flying in 2021 and astronauts heading to a nearby asteroid in 2025, the officials said. From there, NASA hopes to send the rocket and astronauts to Mars and Venus – at first just to circle, but then later landing on the planets – in the 2030s.

The rockets will be 34 stories tall and take off from the Kennedy Space Center in Florida. NASA said in a statement that the SLS will initially carry payloads of between 70 and 100 metric tons with plans to later carry up to 130 metric tons. By comparison, the space shuttle that was retired in July could carry about 27 tons.

Why are they sending both rockets up at once? “Basically, its a cost issue. We can duplicate our manufacturing processes and build the two ships together. And we can see which planet is better for humans – Venus or Mars. It’ll be fun, too.”

The Orion Multi-Purpose Crew Vehicle (MPCV, a six-person capsule aboard the rocket, will be used to carry astronauts.

NASA said that in an effort to reduce cost, the rocket will use the same fuel system — liquid hydrogen and liquid oxygen — for both the core and the upper stage propulsion.